A wide range of medical procedures involves placing objects, such as sensors, tubes, catheters, dispensing devices, and implants, within the body. Real-time imaging methods are often used to assist medical practitioners in visualizing the object and its surroundings during these procedures. However, in many situations, real-time imaging is not possible or desirable. Instead, systems for obtaining real-time spatial coordinates of the internal object are often utilized. Many such position-sensing systems have been developed or envisioned in the prior art.
For example, U.S. Pat. No. 5,983,126, to Wittkampf, whose disclosure is incorporated herein by reference, describes a system in which catheter position is detected using electrical impedance methods. U.S. Patent Application Publications 2006/0173251, to Govari et al., and 2007/0038078, to Osadchy, whose disclosures are incorporated herein by reference, describe impedance-based methods for sensing the position of a probe by passing electrical currents through the body between an electrode on the probe and a plurality of locations on a surface of the body.